1. Technical Field
The present invention relates in general to hard disk drives and, in particular, to an improved system method, and apparatus for preventing the accumulation of excess lubrication in the form of lubricant lines on magnetic media for hard disk drives.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy, glass or a mixture of glass and ceramic, and are covered with a magnetic coating that contains the bit pattern. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute. Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile and micro drive.
A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
As the areal density of magnetic media in hard disk drives increases, the thickness of the lubricant used to coat the media must be decreased to avoid adverse effects on the performance of the disk drives. The thickness of media lubricants has been reduced to such a level (e.g., on the order of 10 Å for some applications) that the uniformity of the lubricant layer is a significant issue.
One particular concern is the formation of wide lubricant “lines” on disks during the lubricant application process. Lubricant lines can be several angstroms thicker than the overall lubricant coating on the disks. The lubricant lines remain on the disks, even after pad burnishing and temperature and/or humidity treatments. These relatively thick lubricant lines are potentially damaging to the flight characteristics of sliders. In addition, lubricant lines cause head smear/lubricant pick-up on the sliders, thereby reducing their durability.
Conventional disk holders produce surface waves in the lubricant bath that cause the lubricant lines to form on the disks. One type of prior art design uses a cover for the bath in an attempt to suppress the magnitude of surface waves. Unfortunately, that design requires precise positioning and careful operation throughout the process, which can cause inadvertent scratches on the disks and give rise to even bigger problems during manufacturing. Although this conventional design is workable, a more effective solution for preventing the formation of lubricant lines on magnetic media would be desirable.